Transmission of music by electromagnetic waves.



. L. DE FOREST. TRANSMISSION OF MUSIC BY ELEGTR'OMAGNETIG WAVES.

APPLICATION FILED 11113.9, 1907. 1,025,908.

Patented May 7, 1912.

2 SHEETSJSHEETII.

L. DE FOREST. I TRANSMISSION OF MUSIC BY ELECTROMAGNETIC WAVES.

APPLICATION FILED MAB.9, 1907.

Patented'May 7, 1912.

BEETS-SHEET 2.

\X/ITN-EEEE; I INVIIHTQFQ- ZIAMQK 1 ofudfiw UNITED STATES PATENT OFFICE.

LEE DE FOREST, OF NEW YORK, N. Y., ASSIGNOR TO DE FOREST RAD-IO TELEPHONE I (10., A CORPORATION OF NEW YORK.

TRANSMISSION OF MUSIC BY ELECTROMAGNETIC WAVES.

Specification of Letters Patent.

Patented. May '7, 1912.

Application filed March 9, 1907. Serial No. 361,478.

To all whom it may concern:

Be it known that 1, LEE nn Fonnsr, a citi of music by means of electromagnetic waves without the use of connecting wires between the transmitting and receiving systems. i

The object of my invention is to produce a system whereby musical sounds may be developed and transmitted by electromagnetic waves at a central distributing point to one or more receiving stations.

My invention will be described in connection with the drawings which accompany and form a part of this specification and which illustratev two arrangements of apparatus and circuits whereby the foregoing objects have been successfully realized in practice; but it is to be understood that many modifications may be made in the particular embodiments of my invention which I herein show and specifically describe Without departing from the principle of said inventionj In the drawings, Figure 1 represents one em; bodiment of the present invention wherein a source of practically-continuous or undamped electrical vibrations is employed, Fig. 2 represents a modification in which the oscillations developed in a sonorous circuit have a spark-frequency comparable with the frequency of the highest note employed in music. Fig. 3 diagrammatically represents a receiving system. v

In the figures, V is an elevated conductor.

M M M M are transformers, of which the primaries and secondaries, respectively, are T L, &c., and I I 1 R R are impedances.

C C are condensers.

D is a source of unidirectional electromotive force. y

A A A A are sources of vibratory -electromotive force.

K K" K are circuit closers.

The circuit S C 1 is an oscillatory circuit provided, with electrodes between which an electric arc may be developed at S when the source D is connected to the terminals of "said electrodes. The impedances R R connected between the source D and the-arc-electrodes prevent any sudden change of current value in the supply circuit and under these conditions, as is now well understood, practicallyc'ontinuous or undamped' electrical oscillations will be developed .in the circuit S C L, the energy of which by the transformer M orby other suitable means may be con veyed to the elevated conductor system V I E and converted into electro-radiant energy.

Operativelygassociated in any suitable way with the source of practically-continuous or undamped electrical oscillations is means for modifying the electrical vibrations in accordance with the-musical sounds to be transmitted. The particular means for so modifying said electrical vibrations which I have illustrated in,Fig. 1 for the purpose of more fully disclosing the present invention is a, circuiflcontaining means for developing vibratoi y electric currents varyingin accordance with the sounds to be transmitted and the particular means shown in said figure whereby said circuit is associated with said source of oscillations is the transformer M provided with the iron core H. The a foresaid circuit is operatively connected with a number of sourcesof vibratory electric current, A A A' which may be alternating current generators which, preferably, develop simple harmonic currents each having a frequency corresponding to the frequency of one of the notes of the musical scale. By means of the circuit closers K K K said, generators may be simultaneously or otherwise connected in series with the primary winding I, of the transformer M and the energy of the currents developed by said generators will modify the oscillations developed by the circuit- S G I in accordance with the musical composition to be transmitted. The oscillationsdeveloped by the circuit S C L in the elevated conductor system will be correspondingly modified and-the electromagnetlc waves rad ated from said system Wlll have the samecharacterlstics as to frcsaid system.

In the system shown in Fig. 2 the circuit S C I is a sonorous circuit energized by the alternator A or other suitable source of 'quency andamplitude as the oscillations in vibratory currents adapted to produce in the circuit'S I electrical oscillations l1aving a spark-frequency comparable with the frequency or rate of vibration of'the highest note employed in music. The circuit which includes the primary 1 of the transformer M? may, as shown, be associated directly with said sonorous circuit which will under the circumstances include the secondary 1 of said transformer. The transformer M is of the air-core type. It will be under stood without further illustration that the circuit including the generators A, &c., may be associated with the circuit S C I, in the same manner as shown in Fig. 1 and that it may be associated with the circuit S C I in the same manner as shown in Fig. 2. The condenser C may be employed as shown in Fig. 1 to shunt the impedance of the generator I) with respect to the vibratory currents developed in the secondary of the transformer M. i

The electromagnetic waves developed by the systems shown in Ifigs. 1 and 2 and Which, although exceeding in frequency the limit of audibilit-y, are modified in amplitude by vibrations corresponding to the sonorous vibrations of the air accompanying the musical sounds to be transmitted,- may be received and their energy converted into vibrations of the air corresponding to the original musical sounds by means of any suitable receiving system. At such receiving system the-energy of the electrical oscillations resulting from the waves received will be converted by means of a wave detector into local circuit currents modified in accordance with the currents produced in the primary circuits of the transformers M and M. The local circuit currents may be translated by a telephone receiver which may be connected to said local circuit with or without the interpositon of a relay, such, for example as that shown in myLetters Patent No. 841,387, dated January 15, 1907. Such a receiving system by way of illustration is shown in Fig. 3 in which V If" E is the elevated receiving conductor system with which may be associated. the tuned receiving circuit I C. F is a wave detector herein shown as an audion, B B are batteries and T is a telephone receiver.

I claim:

1. The method of transmitting musical sounds which consists in developing electrical vibrations having a frequency higher than the limit of audibility, and generating respectively independent electric currents corresponding in frequency to simple harmonic sound waves, successively modifyin the electrical vibrations by said. independ ently generated currents, and transforming the modified electrical oscillations intoclectro-radiant energy.

2..In a system for transmitting musical sounds, an oscillating circuit, means for producing therein practically continuous electrical vibrations having a frequency higher than the limit of au dibility, a modifying circuit associated with said oscillating circuit, a plurality of means arranged in the modifying circuit respectively operating to develop therein electric currents, and means for varying each of said electric currents in accordance with the sound vibrations ofa different musical note.

3. In a system for transmitting musical' sounds, an oscillating circuit, means for producing therein practically continuous electrical vibrations having a frequency higher than the limit of audibility, a modifying circuit associated with said oscillating circuit, a plurality of means arranged in the modifying circuit and respectively operating to develop therein electric currents, means for varying each of said electric currents in accordance with the sound vibrations of a different musical note, and a transformer associating said modifying and oscillating circuits, said transformer having an iron core.

4. In a system for t'ansmitt-ing sounds, an oscillating circuit, means for producing therein electrical vibrations having a high frequency, a modifyingcircuit associated therewith, and means respectively independent of each other, and arranged in the modifying circuit for respectively varying the current therein in accordance with each note of the harmonic scale.

In testimony whereof, I have hereunto subgcribed my name this 6th day of March 190 LEE DE FOREST.

Witnesses H. V. Gonrzn, THOMAS I. GALLAGHER. 

